In recent years, in the field of blood transfusion, a blood transfusion before which mixed white blood cells contained in a blood product have been removed from the blood product, so-called leukapheresis has been spread. This is because it has been revealed that a relatively minor side effect such as headache, nausea, chill, and febrile nonhemolytic transfusion reaction, which are associated with blood transfusion, and a serious side effect such as alloantigen sensitization, viral infection, and graft versus host disease (GVHD) after blood transfusion, which may severely affect some blood recipients, are caused by the white blood cells mixed in the blood product that is used mainly for blood transfusion.
A method for removing white blood cells from a blood product is roughly divided into two types: a centrifugal separation method of separating and removing white blood cells by using a centrifugal separator utilizing the specific gravity difference between blood cell components; and a filter method of removing white blood cells by adhesion or adsorption using a filter material composed of a fiber assembly such as nonwoven fabric, a porous structure having continuous pores, or the like. Between them, the filter method of removing white blood cells by adhesion or adsorption is simply operated, and has an advantage of low cost, and the like, therefore, has been widely spread.
Many of the filter devices for removing white blood cells, which are currently available on the market, are constituted of multiple kinds of filter materials, and in the upstream close to an inlet port of blood, a coarse aggregate-removing filter material for removing aggregates of a blood product is arranged. Further, in the downstream part on the side of an outlet port, a fine white blood cell-removing filter material for removing white blood cells is arranged. The aggregate is made by the aggregation of a red blood cell, a white blood cell, a platelet, fibrin, fibrinogen, other denatured proteins, a fat globule, and the like.
The aggregate is present in the size of from around equal degree to that of a white blood cell in the smallest one to exceeding 1 mm in the largest one, and is enriched in adhesion. Further, as to the aggregate, there is a tendency that the longer the storage time of a blood product is, and/or the lower the storage temperature is, the larger the number of aggregates is, and the larger the size is. Therefore, when a blood product is treated only by a white blood cell-removing filter material without using an aggregate-removing filter material, there may be a case where the white blood cell-removing filter material is clogged with aggregates, and it becomes difficult to maintain the flow rate to be expected.
Further, in order to improve the quality of a blood product, white blood cell removal before storage, which performs the removal of white blood cells on the blood collection day or the next day after the blood collection, has become the mainstream. In recent years, in order to efficiently perform the white blood cell removal, the number of the facilities for performing the removal is reduced, and the number of the blood products treated in one facility is increased. In the facility, because a blood product is collected also from far away, the number of the bloods to be filtered after the refrigerated storage for one day is increased, therefore, the number of the bloods generating aggregates is also increased. Accordingly, during the filtration, flow failure is generated, and when the filtration is stopped, the blood product has to be discarded, therefore, the precious blood product is wasted. Therefore, there is a strong need for a filter to which an aggregate-removing filter material has been introduced.
In order to address such a problem, for example, in Patent Literature 1, a filter device having a structure in which in the upstream of a filter material for removing white blood cells, two or more kinds of the filter materials for removing aggregates, which are selected from the group consisting of nonwoven fabric, woven fabric, and knitted fabric, and have a bulk density different from each other in the range of 0.1 to 1.0 g/cm3, are arranged, and the bulk density of the aggregate-removing filter material is increased on the lower part of the downstream side has been disclosed.
In Patent Literature 2, a filter device composed of multiple kinds of fibrous materials, and defined by XY of an average fiber diameter X and an average fiber interval Y of fibers has been disclosed. This filter device has a structure in which a filter material of XY>50 is arranged in the upstream to capture larger aggregates, a filter material of 50≥XY>7 is arranged in the downstream to capture relatively smaller aggregates, and a filter material of 7≥XY is arranged further in the downstream to remove white blood cells.
In Patent Literature 3, a filter material for removing aggregates in which there are at least two kinds of pore groups of a pore group A having the individual pore diameter of 500 μm or more, and a pore group B having the individual pore diameter of 150 to 500 μm, and the average pore diameter of the pore group A is 600 to 1500 μm, the average pore diameter of the pore group B is 200 to 450 μm, and the opening ratio is 40% or more has been disclosed.
In Patent Literature 4, a filter device in which the first to third elements are contained, and the first element is set as a filter material for removing gel (this is a synonym of a relatively large aggregate), the second element is set as a filter material for removing minute aggregates, and the third element is set as a filter material for removing white blood cells has been disclosed.
In Patent Literature 5, an aggregate-removing filter material composed of spunlace nonwoven fabric using short fibers has been disclosed. Further, In Patent Literature 6, an aggregate-removing filter material using base fabric of long fibers, and using short fibers has been disclosed.